The present invention relates to a straightener with rollers designed in particular for the straightening of steel bars for concrete.
It is known that elongated metal products obtained by rolling and in particular steel bars for concrete, require straightening before use to bring them into true.
In practice it is difficult to achieve perfect straightening because of constraints of all kinds which exists in the product to be straightened before being introduced into the straightener.
Straighteners which operate by alternating flexion in the same plane are already known. The straighteners circulate the wire to be straightened between rollers which are on either side of the axis of the machine which causes alternating flexion resulting in the elastic limit of at least part of the section of the product to be straightened to be exceeded by subjecting it to permanent deformations which diminish progressively to reach a virtually nil value as the product to be straightened passes through the straightener.
It is also known that to achieve satisfactory straightening it is necessary to regulate precisely the position of the various rollers relative to the axis of the progress of the product to be straightened, and also the distance separating the various rollers along the axis of the straightener.
The result is a considerable waste of time and considerable difficulty in adjustment when the straightener has to deal successively with products of different diameter.
This disadvantage is particularly serious in the case where the product to be straightened consists of steel bars for concrete which have dimensional characteristics that can vary quite considerably in the same lot.
Devices known from U.S. Pat. No. 4,719,781 permit the simultaneous displacement and adjustment of several rollers in order to adapt the straightener to the dimensional characteristics of the product to be straightened, but to date these devices do not give complete satisfaction because they do not take into account all the adjusting required to obtain satisfactory straightening.
Furthermore, these known devices do not in general permit the axis of the straightened product to be kept in a fixed position when the setting of the rollers is modified to take into account the dimensional variations of the product that is to be straightened, when entails adjustment of the devices upstream and downstream of the straightener, or failing this an alteration of the straightness of the product.
It is also known that to obtain correct straightening it is necessary to apply successive alternating flexion in at least two different planes.